Nylons are polyamides which are generally synthesized by the condensation polymerization of a diamine with a dicarboxylic acid. Similarly, Nylons may be produced by the condensation polymerization of lactams. A ubiquitous nylon is Nylon 6,6, which is produced by condensation polymerization of hexamethylenediamine (HMD) and adipic acid. Nylon 6 can be produced by a ring opening polymerization of caprolactam (Anton & Baird, Polyamides Fibers, Encyclopedia of Polymer Science and Technology, 2001).
Biotechnology offers an alternative approach to petrochemical processes via biocatalysis. Biocatalysis is the use of biological catalysts, such as enzymes, to perform biochemical transformations of organic compounds.
Both bioderived feedstocks and petrochemical feedstocks are viable starting materials for the biocatalysis processes.
Accordingly, against this background, it is clear that there is a need for sustainable methods for producing one or more of adipic acid, 6-hydroxyhexanoate, 6-aminohexanoate, hexamethylenediamine and 1,6-hexanediol (hereafter “C6 building blocks”) wherein the methods are biocatalyst based.
However, no wild-type prokaryote or eukaryote naturally overproduces or excretes such C6 building blocks to the extracellular environment. Nevertheless, the metabolism of adipic acid has been reported.
The dicarboxylic acid adipic acid is converted efficiently as a carbon source by a number of bacteria and yeasts via β-oxidation into central metabolites. β-oxidation of Coenzyme A (CoA) activated adipate to CoA activated 3-oxoadipate facilitates further catabolism via, for example, pathways associated with aromatic substrate degradation. The catabolism of 3-oxoadipyl-CoA to acetyl-CoA and succinyl-CoA by several bacteria has been characterized comprehensively
The optimality principle states that microorganisms regulate their biochemical networks to support maximum biomass growth. Beyond the need for expressing heterologous pathways in a host organism, directing carbon flux towards C6 building blocks that serve as carbon sources rather than as biomass growth constituents, contradicts the optimality principle. For example, transferring the 1-butanol pathway from Clostridium species into other production strains has often fallen short by an order of magnitude compared to the production performance of native producers (Shen et al., Appl. Environ. Microbiol., 2011, 77(9):2905-2915).
The efficient synthesis of the seven carbon aliphatic backbone precursor is a key consideration in synthesizing one or more C6 building blocks prior to forming terminal functional groups, such as carboxyl, amine or hydroxyl groups, on the C6 aliphatic backbone.